Thermoplastics such as PP (polypropylene), PE (polyethylene), etc., are normally coloured using pigment concentrates which are usually called masterbatches or compounds. These concentrates are prepared by mixing ingredients together and subjecting them to any of the processes commonly used for dispersing particulate solids in a thermoplastic polymer. Compounding or mixing in a twin-screw extruder is one of these processes. Pigment concentrations in these masterbatches may be from 20-70% and other additives may be present such as waxes, dispersants, lubricants and UV stabilisers.
Production of a masterbatch requires that the pigment is dispersed optimally in the thermoplastic polymer, i.e., fine particles with few aggregates. Problems can arise in the production of masterbatches if aggregates are present as this will lead to filter blocking of the extruder. The pigment concentrates are used to colour thermoplastic film, fibres and solid articles. Particular requirements are needed on the quality of these finished articles, for instance, in solid articles good dispersion of the pigment in order to maximize colour development, tinctorial strength and reduced speck: levels are also required. For films, incomplete dispersion of the pigment can lead to cracking, unwanted light scattering effects and specks. In fibres, incomplete dispersion of the pigment will result in filter blocking of the extruder and fibre breakage.
Waxes are used to disperse particulate solids in thermoplastic polymers. However, the waxes only wet the pigments and do not disperse them into a stable dispersion. Also, waxes are prone to migration to the surface of the thermoplastic article.
U.S. Pat. No. 3,778,287 discloses structures of poly 12-hydroxystearic acids (PHS) and polyricinoleic acids (PRA) and their use in aliphatic/aromatic ink/paint systems as dispersants for organic and inorganic pigments.
U.S. Pat. No. 4,797,400 discloses the use of the polymer containing a carboxylate functionality, e.g., poly(12-hydroxystearic acid) or polyricinoleic acid, as a dispersant in the presence of a particulate solid, a lubricant and a thermoplastic polymer.
British Patent 2 056 461 attempts to incorporate a dispersant onto a filler by employing poly 12-hydroxystearic acid or polyricinoleic acid.
U.S. Pat. No. 3,748,308 discloses polyesters containing carboxy groups and the polyesters are used as dispersing agents in organic liquids. These compounds contain aromatic diacids or anhydrides to generate the carboxy groups, and diol/triols for multiplicity.
International Publication WO 05/097872 discloses polyesters containing carboxy groups and used as dispersing agents for pigment concentrates for colouring thermoplastics. These agents contain diacids or anhydrides to generate the carboxy groups, and a mono, di or triol.
Fatty acid initiated polycaprolactone polymers are disclosed as intermediates to polyethylene imine dispersants in U.S. Pat. Nos. 4,645,611; and 4,861,380. The fatty acids disclosed therein have not been employed as a dispersant.